JS04.6.A The landscape of tumor cell states and spatial organization in H3-K27M mutant diffuse midline glioma across age and location

Background

Histone 3 lysine27-to-methionine mutations (H3-K27M) frequently occur in childhood diffuse midline gliomas (DMGs) of the pons, thalamus and spinal cord, presumed to be driven by the specific spatiotemporal context of these midline locations during postnatal development. While most common in the pons and at mid-childhood ages, the same oncohistone mutation is recurrently detected in adult DMGs and throughout different midline regions. The potential heterogeneity of tumors at different ages and in different anatomical locations of the midline are vastly understudied.

Material and Methods

Through dissecting the transcriptomic, epigenomic and spatial architectures of a comprehensive cohort of patient H3-K27M DMGs - spanning the age range from 2-68 years and locations from spinal cord to thalamus - at single cell resolution, we delineate how age- and location-dependent contexts shape glioma cell-intrinsic and -extrinsic features in light of the shared driver mutation.

Results

We identify that oligodendrocyte precursor (OPC)-like cells constitute the stem-like compartment in H3-K27M DMGs across all clinico-anatomical groups, however, depending on location, display varying levels of maturity resembling less differentiated pre-OPCs or more mature OPCs further differentiated along the oligodendroglial lineage. We further demonstrate increased mesenchymal cell states in adult tumors, which we link to age-related differences in glioma-associated immune cell compartments. We for the first time resolve the spatial organization of H3-K27M DMG cell types in intact patient tissues, identifying a local niche of the oligodendroglial lineage.

Conclusion

Our study provides a powerful resource for rational modeling and therapeutic frameworks taking into account determinants of age and location in this lethal glioma group.

94 Myostatin gene editing by CRISPR/Cas9 technology of Brangus fetal fibroblasts to produce edited embryos by cloning

Some European cattle breeds, such as Charolais and Maine Anjou, have natural mutations in the myostatin gene (MSTN) that inhibit its expression and result in an increase in muscle mass and protein content. An innovative hallmark would be the invitro introduction of this genotype in South America cattle breeds to improve their commercial value. To achieve this, we aimed to disrupt MSTN gene expression in bovine fetal fibroblasts (BFFs) using CRISPR/Cas9 technology and to generate MSTN-edited embryos by somatic cell nuclear transfer (SCNT). BFFs were isolated from a cloned fetus of a Brangus bull with a prized genetic background and nucleofected with the Cas9 ribonucleoprotein-gRNA complex previously assessed to target exon 2 of the bovine MSTN gene. To evaluate MSTN editing, genomic DNA from the wild-type (WT) and nucleofected BFFs were isolated, exon 2 of MSTN was amplified by PCR, and the PCR product was Sanger sequenced. In all cases, the sequencing results were analysed using the indel Synthego software tool. According to indel analysis, MSTN gene editing efficiency of the BFFs was 58.83%±3.2 (n=6). The resulting edit consisted of insertion of thymine in exon 2 of the MSTN gene that shifted the gene reading frame, introducing a premature stop codon and generating a truncated MSTN protein. The nucleofected BFFs were then used to generate embryos by SCNT, and WT BFFs were included as controls. Embryo cleavage and blastocyst development rates were evaluated at Day 2 and 7, respectively (Chi-squared test, P<0.05). Although lower cleavage rates were obtained in the MSTN-edited BFFs group [65.3% (n=273/418) vs. 87.6% (n=169/193)], no differences were observed at the blastocyst stage [19.1% (n=80/418) vs. 25.4% (n=49/193)]. To confirm the efficiency of MSTN editing in the cloned embryos, 10 blastocysts generated with the MSTN-edited BFFs were individually analysed for MSTN exon 2 sequence as described before. The results showed that 30% of the blastocysts (3/10) presented a homozygous biallelic edition, which consisted of a thymine base insertion, as expected. In summary, the strategy we used allowed production of MSTN null cloned Brangus embryos avoiding putative undesired integration of exogenous DNA into the bovine genome, such as plasmid sequence, regardless of off-target occurrences. We conclude that CRISPR/Cas9 is an efficient technique to disrupts MSTN gene expression in bovine embryos; this work represents a step toward improving the production efficiency of South American cattle breeds.

146 HEPARAN SULFATE IS INVOLVED IN NUCLEAR SPERM DECONDENSATION AFTER FERTILIZATION IN BOVINE

Reduced glutathione (GSH) is an endogenous disulfide bond reducer present in mammalian oocytes. It plays a critical role in sperm decondensation following fertilization, disrupting the protamine bonds that sustain the hypercondensed state of sperm DNA. However, disulfide bond reduction needs to be followed by protamine removal to achieve male pronuclear formation. In humans, heparan sulfate (HS) has been shown to exert this role (Romanato et al. 2008 Hum. Reprod. 23, 1145–1450). Although there are no reports in bovine, we recently demonstrated the presence of HS in cow oocytes by indirect immunofluorescence, using a specific anti-HS monoclonal antibody (Canel et al. 2015, Proc. SSR 48th Annual Meeting). Heparinases are known to cleave HS chains selectively, leading to its depolymerization. In the present work, we analysed the possible role of HS as protamine acceptor after fertilization in cattle. To this aim, we directly injected heparinase into the cytoplasm of IVF presumptive zygotes, and analysed its effect on pronuclei formation. Cumulus-oocyte complexes were collected from slaughtered cow ovaries and matured in vitro under standard conditions (Canel et al. 2012 Cell. Div. 7, 23–33). After 21 h, IVF was performed following Brackett and Oliphant’s protocol (1975 Biol. Reprod. 12, 260–274), using frozen–thawed semen from 1 or 2 bulls at a final concentration of 15 × 106 spermatozoa/mL (5 replicates). After 5 h of incubation, cumulus cells and sperm bound to zona pellucidae were removed from presumptive zygotes. Heparinase III solution (H8891, Sigma, St. Louis, MO, USA) was diluted in 50% (vol/vol) polyvinylpyrrolidone solution in PBS-(polyvinylpyrrolidone) at a final concentration of 50 U mL−1 and ~30 pL was mechanically injected into the cytoplasm of each IVF presumptive zygote (Hep group) using a 9-μm inner diameter injection pipette. A group of zygotes was injected with the same volume of 10% polyvinylpyrrolidone (sham), whereas others were not subjected to injection (control). All zygotes were cultured for 16 h from the beginning of IVF in SOF medium (Holm et al. 1999 Theriogenology 52, 693–700). For pronuclear formation assessment, presumptive zygotes were permeabilized with 0.2% Triton X-100 for 15 min at room temperature, and their DNA content was stained with 5 µg mL−1 propidium iodide and observed under an epifluorescence microscope. Zygotes showing 2 pronuclei (PN) were considered as synchronically fertilized, whereas those showing one PN and one condensed sperm head were considered as asynchronically fertilized. Data were analysed by Fisher’s exact test (P < 0.05). The rate of IVF zygotes showing 2 PN was lower for the Hep group (60.3%, n = 131) than those from sham (94.1%, n = 119) and control groups (98%, n = 101), which did not differ between them (P < 0.05). In conclusion, our results show for the first time that HS is involved in bull chromatin sperm decondensation and allow us to propose HS as a putative protamine acceptor during male pronucleus formation after IVF in cattle. Given the high frequency of sperm decondensation failure observed in bovine after intracytoplasmic sperm injection, this work provides new insights for the development of novel sperm/egg treatments that might improve intracytoplasmic sperm injection outcomes in cattle.